Kind of depends on their "death roll" ability, I think. I had a sen that took an algae chip on a death roll when he was only 3". After I picked myself off the floor from laughing I started giving him feeder guppies from my 20 occasionally, he was fine, never choked. It did take him a while to figure out how to catch them though, first two were in there two weeks before he caught and ate both the same night, greedy little guy he was.
My current pair I have never seen death roll anything, so I'm kind of leery about feeders even though they're both almost 5".